Tattoos can cause cancer and mutations - and one colour is potentially more toxic than others, according to scientists.

Research by the European Chemicals Agency to be published imminently is investigating possible risks associated with being inked.

The agency said: "Many reports show significant concerns for public health stemming from the composition of inks used for tattooing.

"The most severe concerns are allergies caused by the substances in the inks and possible carcinogenic, mutagenic or reproductively toxic effects."

Inks are not currently regulated in the EU. If any particular chemicals are found to be harmful as thought, they will be banned.

An agency spokesman said: "If it is found that a restriction is needed, a formal proposal to restrict the substances will be submitted within one year to initiate the process."

Red ink has been linked to dermatitis - swelling and soreness - due to it containing mercury sulphide.

Meanwhile red, blue, green and purple ones are more likely to cause granulomas – little ridges of bumps on the skin.

The public will be asked to contribute to the research. The NHS has also warned of the dangers of ‘black’ or ‘neutral’ henna.

Different to authentic henna, which is orange in colour, this darker substance it may contain levels of a chemical dye ‘so powerful and toxic that it is illegal to use it on the skin’.

The NHS warned: "If you see a shop or stall offering to paint black tattoos onto your skin, don’t be tempted to get one. It could leave you scarred for life and put you at risk of a life-threatening allergic reaction."

Anyone suffering an allergic reaction should contact a doctor as soon as possible.